Small information devices, such as a mobile phone, a personal digital assistant (PDA), and the like, have been required to have security due to their high specification. As communication speed increases, the frequency of storing information in a remote server and accessing the server over a network gradually increases. In order to access the information that requires security, authentication is necessary in the small information devices. Examples of a range in which high-level security is required include the financial transactions field, such as mobile banking and a digital wallet.
Methods of ensuring security in the small information devices include personal authentication using a password, identification (ID) card, or the like. However, the password or the ID card is at a high risk of being stolen. Thus, in fields, such as financial transactions, and the like, more enhanced personal authentication (authentication of the user of the device to which the user is previously registered) is required. In order to respond to the demand, biometric information is increasingly used, and fingerprints among biometric information are mainly used for convenience.
However, in the case of fingerprints, there is a problem that authentication may fail due to counterfeit fingerprints formed of silicone or gummies. To solve the problem of fingerprints, there is a proposal to use various types of biometric information including the iris, blood flow, impedance, or the like. Some types of biometric information have been implemented technically, but for financial reasons, have not become commercially popularized yet.
In non-patent document 1 below, there is proposed technology of authenticating a human body by using a characteristic that an input power with multiple frequencies is applied to the human body and impedance magnitude and phase of the human body vary with frequency change. A brief summary of the known biometric authentication technology using impedance is that biometric authentication is possible by applying voltage to the human body with varying frequency and by measuring the impedance magnitude and phase of the human body according to the frequency change. As shown in the conventional technology, in order to authenticate the human body using impedance, it is necessary to have (1) a circuit for applying the with input power multiple frequencies and (2) a circuit for measuring the impedance magnitude and phase of the human body according to each frequency. Particularly, in order to measure the impedance magnitude and phase, a measurement signal is multiplied by sine sinusoidal waves and cosine sinusoidal waves, the result is passed through a low pass filter, and the real part and the imaginary part of impedance response are obtained and used in measuring the magnitude and phase. Construction of the circuit with reliability level results in complexity in hardware configuration, and thus there is a difficulty in popularization.